1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to cooperative transceiving by wireless interface devices of the same host device.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etcetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
The 2.4 GHz industrial, scientific and medical (ISM) band is experiencing unprecedented growth due mostly to strong showing of two wireless technologies: wireless local area networking (WLAN) and wireless personal area networking (WPAN). WLAN operates in the 100+ meters range and is usually used to augment traditional wired networking by providing wireless connectivity in the home, office or public areas. WLAN devices operate in accordance with IEEE 802.11 standards (802.11b, 802.11 g and 802.11n) and offer data rates in excess of 100 Mbps. In recent years as the voice over IP (VoIP) finds wider adoption for carrying telephone traffic, various new concepts such as Unlicensed Mobile Access (UMA) have been using WLAN as a technology of choice for the wireless terminals.
The WPAN technology is led by Bluetooth that has been designed as a cable replacement technology to provide device interconnection in the radius of approximately 10 meters. The Bluetooth network is organized as a piconet with a single master device and a number of slave devices which are only allowed to communicate with the master. In this scheme a single slave device selected by the master may transmit while others must wait for their turn. The Bluetooth physical layer (PHY) uses frequency hopping spread spectrum (FHSS) technology. At any point in time Bluetooth signal occupies just 1 MHz of bandwidth but the center frequency changes up to 1600 times per second. The frequency change (hopping) pattern is selected by the piconet master such that the interference between different piconets is minimized. A time-division duplex (TDD) technique is used to transmit and receive data in a piconet. The transmission channel is divided into 625 us slots. Piconet master transmits during even-numbered slots while the slave devices transmit during odd-numbered slots. The specification also allows multislot transmissions where packets occupy multiple consecutive slots (three or five). A slave must respond to the master's packet addressed to it. If it has no data it must respond with a NULL packet. The Bluetooth specification defines the following types of links for the support of voice and data applications: synchronous connection-oriented (SCO), extended synchronous (eSCO) and asynchronous connectionless (ACL). SCO and eSCO links are typically used for transmitting real-time voice and multimedia packets while ACL is most often used for non-real time data traffic. The SCO packets do not have cyclic redundancy check (CRC) protection and are never retransmitted. eSCO and ACL packets use CRC and errors are corrected by packet retransmission. The most typical Bluetooth application is found in the wireless headsets.
WLAN technologies are lead by IEEE 802.11 that defines two different ways to configure a wireless network: ad hoc mode and infrastructure mode. In ad hoc mode, nodes are brought together to form a network on the fly, whereas infrastructure mode uses fixed access points (AP) through which mobile nodes can communicate. These network access points are usually connected to wired networks through bridging or routing functions.
The WLAN medium access control (MAC) layer is a contention-resolution protocol that is responsible for maintaining order in the use of a shared wireless medium. IEEE 802.11 specifies both contention-based and contention-free channel access mechanisms. The contention-based scheme is also called the distributed coordination function (DCF) and the contention free scheme is also called the point coordination function (PCF). The DCF employs a carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this protocol, when the WLAN MAC receives a packet to be transmitted from its higher layer, the MAC first listens to ensure that no other node is transmitting. If the channel is clear, it then transmits the packet. Otherwise, it chooses a random backoff factor that determines the amount of time the node must wait until it is allowed to transmit its packet. During periods in which the channel is clear, the WLAN MAC waiting to transmit decrements its backoff counter, and when the channel is busy, it does not decrement its backoff counter. When the backoff counter reaches zero, the WLAN MAC transmits the packet. Because the probability that two nodes will choose the same backoff factor is low, collisions between packets are minimized. Collision detection, as employed in Ethernet, cannot be used for the radio frequency transmissions of devices following IEEE 802.11. The IEEE 802.11 nodes are half-duplex—when a node is transmitting, it cannot hear any other node in the system that is transmitting because its own signal drowns out any others arriving at the node.
Optionally, when a packet is to be transmitted, the transmitting node can first send out a short request to send (RTS) packet containing information on the length of the packet. If the receiving node hears the RTS, it responds with a short clear to send (CTS) packet. After this exchange, the transmitting node sends its packet. If the packet is addressed to a single recipient (directed packet) is received successfully, as determined by a cyclic redundancy check (CRC), the receiving node transmits an acknowledgment (ACK) packet. If the transmitting node does not receive an ACK for the directed packet it assumes that the packet transmission had failed and error recovery is attempted by retrying the original packet. Retries are continued until either the ACK packet is received or the retry limit is reached. In the later case the packet is retried at a lower data rate and if that fails the packet is discarded.
To maintain a reliable data connection at the highest possible data rate the WLAN transmitter usually employs dynamic rate adaptation algorithm. Such algorithm reduces the data rate for wireless communication when number of unsuccessful attempts to transmit a packet reaches a certain threshold. In an environment where the thermal noise is the only source of receive errors this algorithm converges to the highest data rate supported by the wireless link. However for the cases where transmission failed due to the interference from a Bluetooth transceiver collocated with the receiving node this rate adaptation algorithm would result in lowering the data rate, increasing the packet transmission time and thus further increasing the probability of the interference errors.
When the packet is lost the overall network performance is affected. The impact is dependent on the type of packets. Discarding directed frames might result in poor voice quality in VoIP link or lower TCP throughput. If a wireless station fails to receive multicast packets might result is failures in such protocols as ARP and DHCP. Loosing beacon frames might result in loss of synchronization to the wireless network.
As WLAN and WPAN are designed for different uses they often complement each other in personal computers and mobile devices such as phones and personal digital assistants. And while these two wireless systems use different technologies they operate in the same 2.4 GHz ISM band and as a result interfere with each other. The problem of Bluetooth interfering with WLAN is particularly serious when these two technologies are implemented on a single chip and share some of the radio components. Such interference might cause degraded data throughput, reduced voice quality or even link disconnection.
The interference between WLAN and WPAN networks can be divided into two classes. The interference is said to be external if the interfering devices are physically separated by a distance of more than two meters. The interference is said to be internal if the devices are located at a distance of less than two meters and devices are said to be collocated. The internal interference is much more severe as each wireless transceiver has drastic impact on the performance of the other, as it's transmit/receive activity may saturate the LNA of the other device.
The mutual interference between BT and WLAN depends on several factors. The physical distance between BT and WLAN, the operating data rate, operating transmit power levels and amount of data all affect the interference. To address the problem of mutual interference between 802.11 WLAN and Bluetooth technologies IEEE has developed 802.15.2 Recommended Practice that offers several coexistence mechanisms to enable WLAN and Bluetooth to operate in a shared environment without adversely affecting each others performance. The IEEE 802.15.2 Recommended Practice categorizes coexistence mechanisms into two classes: collaborative and non-collaborative. The former is applicable to collocated WLAN and Bluetooth and requires exchange of information between these two devices, while the later does not require information sharing.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention.